Anionic polymerization of conjugated dienes with lithium initiators, such as sec-butyllithium, and hydrogenation of residual unsaturation has been described in many references. The capping of mono-initiated and di-initiated living anionic polymers to form functional end groups is described in U.S. patent application Ser. No. 938,917 filed Aug. 31, 1992 (T3229).
Anionic polymerization using protected functional initiators having the structure R.sup.1 R.sup.2 R.sup.3 Si-O-A'-Li is described in U.S. No. 5,331,058 wherein R.sup.1, R.sup.2, and R.sup.3 are preferably alkyl, alkoxy, aryl, or alkaryl groups having from 1 to 10 carbon atoms, and A' is preferably a branched or straight chain bridging group having at least 2 carbon atoms. Polymerization with such a protected functional initiator, followed by capping to produce a second terminal functional group, produces telechelic polymers which otherwise can be prepared by capping polymers prepared with difunctional initiators such as 1,4 dilithiobutane and lithium naphthalide. The use of a protected functional group avoids the formation of ionic gels which occur when diinitiated polymers are capped with reagents such as ethylene oxide. These gels form even in relatively polar solvent mixtures and hinder subsequent processing steps.
One way to prepare difunctional telechelic polymers without forming a gel is to use a protected functional initiator such as the structure: ##STR1## wherein A" is cyclohexyl or -CR'R"-, wherein R' is a linear alkyl having from 1 to 10 carbon atoms and R" is hydrogen or a linear alkyl having from 1 to 10 carbon atoms. The compounds of structure (A) initiate polymerization of anionic polymers at high polymerization temperatures. The protected functional group survives hydrogenation of conjugated diene polymers and is readily removed by hydrolysis in the presence of methanesulfonic acid. The initiators of structure (A) can be used to make telechelic polymers by capping with ethylene oxide or oxetane. However, oxetane is not readily available on a commercial scale and ethylene oxide can be hazardous due to its reactivity and toxicity.
A recent publication by M. A. Peters and J. M. DeSimone (Polym. Prepr. (Am. Chem. Soc. Div. Polym. Chem.), 1994,35(2), 484) describes the preparation of mono- and di-functional polymers by capping mono-initiated and di-initiated living anionic polymers with a chlorosilane of the following structure: ##STR2## instead of ethylene oxide or oxetane. In this process, LiC1 is eliminated and the protected alcohol group is added to the polymer chain end, avoiding gel formation.